This invention relates to a motor drive amplifier and, more particularly, to an amplifier for use in driving the motor of a video tape recorder/player.
Prior art motor drive circuits typically utilize a square wave signal to drive the motors. It is principally only the fundamental of the square wave which is the main driving force. The harmonics of the square wave produce no driving force and are simply wasted as heat. Furthermore, most prior art motor drive amplifiers have a standing current which can lead to thermal run away. Again, this results in inefficiency and wasted energy. Still another problem with prior art motor drive circuits is time delay in the output stages of the motor drive amplifier. Each additional stage of amplification increases the time delay of the signal passing through. This translates into a narrower bandwidth than might otherwise be available because as the time delay begins to approach one-half of the period of the input signal waveform (i.e. a 180.degree. phase shift) the "negative" feedback circuit of the amplifier is supplying positive feedback, thereby causing oscillation.